/*
 * Copyright (c) 2018-2020 "Graph Foundation,"
 * Graph Foundation, Inc. [https://graphfoundation.org]
 *
 * This file is part of ONgDB.
 *
 * ONgDB is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
/*
 * Copyright (c) 2002-2020 "Neo4j,"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.graphalgo.impl.ancestor;

import java.util.LinkedList;
import java.util.List;

import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.PathExpander;
import org.neo4j.graphdb.Relationship;
import org.neo4j.graphdb.ResourceIterator;
import org.neo4j.helpers.collection.Iterators;

import static org.neo4j.graphdb.traversal.BranchState.NO_STATE;
import static org.neo4j.graphdb.traversal.Paths.singleNodePath;

/**
 * @author Pablo Pareja Tobes
 */
public class AncestorsUtil
{
    private AncestorsUtil()
    {
    }

    /**
     *
     * @param nodeSet Set of nodes for which the LCA will be found.
     * @return The LCA node if there's one, null otherwise.
     */
    public static Node lowestCommonAncestor( List<Node> nodeSet, PathExpander expander )
    {
        Node lowerCommonAncestor = null;
        if ( nodeSet.size() > 1 )
        {
            Node firstNode = nodeSet.get( 0 );
            LinkedList<Node> firstAncestors = getAncestorsPlusSelf( firstNode, expander );
            for ( int i = 1; i < nodeSet.size() && !firstAncestors.isEmpty(); i++ )
            {
                Node currentNode = nodeSet.get( i );
                lookForCommonAncestor( firstAncestors, currentNode, expander );
            }
            if ( !firstAncestors.isEmpty() )
            {
                lowerCommonAncestor = firstAncestors.get( 0 );
            }
        }
        return lowerCommonAncestor;
    }

    private static LinkedList<Node> getAncestorsPlusSelf( Node node, PathExpander expander )
    {
        LinkedList<Node> ancestors = new LinkedList<>();
        ancestors.add( node );
        ResourceIterator<Relationship> relIterator =
                Iterators.asResourceIterator( expander.expand( singleNodePath( node ), NO_STATE ).iterator() );
        while ( relIterator.hasNext() )
        {
            Relationship rel = relIterator.next();
            node = rel.getOtherNode( node );
            ancestors.add( node );
            relIterator.close();
            relIterator = Iterators.asResourceIterator( expander.expand( singleNodePath( node ), NO_STATE ).iterator() );
        }
        return ancestors;
    }

    private static void lookForCommonAncestor( LinkedList<Node> commonAncestors, Node currentNode,
            PathExpander expander )
    {
        while ( currentNode != null )
        {
            for ( int i = 0; i < commonAncestors.size(); i++ )
            {
                Node node = commonAncestors.get( i );
                if ( node.getId() == currentNode.getId() )
                {
                    for ( int j = 0; j < i; j++ )
                    {
                        commonAncestors.pollFirst();
                    }
                    return;
                }
            }
            try ( ResourceIterator<Relationship> relIt = Iterators.asResourceIterator(
                    expander.expand( singleNodePath( currentNode ), NO_STATE ).iterator() ) )
            {
                if ( relIt.hasNext() )
                {
                    Relationship rel = relIt.next();
                    currentNode = rel.getOtherNode( currentNode );
                }
                else
                {
                    currentNode = null;
                }
            }
        }
    }
}
